This invention relates to the handling and treating of aggregates such as mixtures of sand and cement flowing through a conduit or hose and embraces the art of shotcreting or guniting in which the dry aggregate is injected with water and sprayed into position from a nozzle.
Since its inception, the art of spraying aggregates such for example as wet concrete has involved the use of a fluid body through which the dry mix is passed at high velocity and within which a fluid, typically water, is injected into the mix which is then sprayed from the nozzle as a wet concrete mix capable of adhering on surfaces to harden into a structural part. The proportions of fluid and aggregate must be controlled with absolute precision. If the sprayed mix is too dry, it bounces from its target and if too wet, will not remain in place to harden. The injection of fluid into the aggregate has been accomplished heretofore by means of fluid or water rings having an axial central opening through which the dry aggregate is passed. An array of precision radial bores or ducts drilled through the ring to surround the axis of aggregate flow are connected at their outer ends to a pressurized fluid manifold to spray the fluid against the aggregate flowing within. The fluidized aggregate then flows through a mixing area which typically expands and contracts the diameter of the flowing mix after which it is passed through a discharge nozzle at high speed directed at a target form. The small fluid ducts are prone to clogging at both ends with particulate matter which can be carried either in the fluid or in the aggregate and when clogged, are often difficult to clean. Moreover, the circumferential spacing of the drilled ducts can result in dry patches in the mix because of the extremely short time interval between the injection of the fluid and the discharge from the nozzle and the susceptibility to changes in the pressure differential between the fluid and the aggregate. The prior art devices are particularly difficult to use and control when the aggregate is injected with unpolymerized plastic to form concrete which is resistant to corrosion and erosion.